1. Field of the Invention
The subject invention is directed to fuel injectors, and more particularly, to a cost-effective method of forming a large diameter fuel feed passage in the feed arm of a fuel injector employed in a gas turbine engine.
2. Background of the Related Art
In designing fuel nozzles for gas turbine engines, it is desirable to increase fuel passage convection or heat transfer coefficients so as to reduce the wetted wall temperatures within the fuel feed passage. This serves to lower the operating temperatures of the fuel nozzle, which in turn, reduces the potential for fuel coking and carbon formation within the fuel feed passage. Fuel coking within the nozzle can cause reductions in fuel flow. This can lead to undesirable thermal gradients within the combustion system causing hardware distress and ultimately failure.
Typically, to control the wetted wall temperature in the fuel passage of a fuel injector, the diameter of a fuel passage is minimized. This causes higher fuel flow velocities and heat transfer coefficients for a given fuel flow rate and fuel temperature. However, as the diameter of the fuel passage decreases to reduce wetted wall temperatures, the pressure drop through the fuel passage increases undesirably. When combined with the manufacturing challenges and inefficiencies associated with machining small diameter passageways, it is clear that there are significant disadvantages in such a design.
Another method of reducing wetted wall temperatures in a fuel nozzle is disclosed in U.S. Pat. No. 6,457,316. Here, contoured swirl vanes extend from or are otherwise integrally formed with the surfaces of the fuel supply tubes of the nozzle. The contoured swirl vanes accelerate the fuel flowing through the tubes. The swirl velocity induced by the vanes increases the convection coefficient, which in turn, facilitates a reduction in wetted wall temperatures downstream from the swirl vanes. The contoured swirl vanes, like the small diameter passages described above, present manufacturing challenges.
It would be beneficial therefore, to provide a method of forming a fuel feed passage in a fuel injector that overcomes the manufacturing challenges and inefficiencies associated with the prior art, while effectively reducing the wetted wall temperatures within the fuel feed passage of the injector so as to improve turbine efficiency.